function vecA=vec(A)
%Name   : VEC
%         vecA=vec(A)
%Purpose: vectorize Matrix A (L�tkepohl, 1996, Chapter 7)
%Input  : (m x n) matrix A
%Output : (mn x 1) vector vecA
%Author : Ulrich Woitek, 11.7.2005
vecA=reshape(A,prod(size(A)'),1);
